As an enhancement to conventional macro enhanced NodeBs (macro eNBs) for bigger macro cells, Home base stations, Home NodeBs, Femto eNodeBs (eNBs) or any type of home access device (in the following referred to as “HNB”) have become a widely discussed topic within 3rd Generation Partnership Project (3GPP) as well as in the operator and manufacturer community. When deployed in homes and offices, HNBs allow subscribers to use their existing handsets—in a building—with significant improved coverage and increased broadband wireless performance. Moreover, Internet Protocol (IP) based architecture allows deployment and management in virtually any environment with broadband Internet service.
In current standardization activities, deployment scenarios involving Femto Base Stations in the context of 3G and LTE is attracting great interest from manufacturers and operators. The current status in 3GPP standardization activities is that HNB deployment has been acknowledged by several working groups and official documents have been drafted to capture the requirements concerning such HNB deployments.
In 3GPP specification TS 22.220, local IP access in home based networks has been described, wherein local IP breakout (LBO) from HNB to home based networks or to the Internet has been suggested in addition to ordinary IP based services via the operator's core network. Allowing for local breakout (also referred to as “route optimization”) of IP traffic could both shorten the end-to-end route and reduce the load on relatively expensive IP backbones (which inherently provides a high quality of service).
Local IP access is intended to differentiate user's local IP traffic in the HNB so that local IP traffic to/from IP devices connected to home based networks is forwarded on the shortest path so that it does not transit outside the home based network (i.e. remains Intranet traffic). Moreover, local IP access traffic to the Internet does not necessarily transit across the operator's evolved packet core (EPC), i.e., the Internet traffic can be forwarded to and received from the Internet via a gateway local to a base station without having to transit through the operator's core nodes.
The current 3GPP specifications and contributions suggest integrating a General Packet Radio Services (GPRS) Gateway Support Node (GGSN) or another kind of gateway function into the HNB for implementing local breakout to home based networks or to the Internet. However, implementing a local gateway for local IP access into the HNB requires incorporation of lots of gateway functions (such as tunneling, charging, Home Agent etc.), so that complexity and processing load is increased and an agreed split between radio access network (RAN) and core net-work is violated. Furthermore, gateway devices are modelled as IP routers that perform IP lookup for routing user traffic to/from 3GPP specified bearer services. Thus, if local breakout was done at a GGSN-like IP router function in the HNB, this would lead to the disadvantage that every kind of inter HNB handover will result in a change of GGSN and thus require use of a cell reselection procedure. In other words, modelling a local gateway functionality within the HNB as an IP router would limit IP mobility and session continuation to work just when the served terminal device (e.g. user equipment (UE)) is connected to the current HNB. This would lead to a severe limitation e.g. in local area scenarios like in an office or campus where local IP access could be served through a multiple cells or base stations in the local area.
Moreover, the local gateway functionality within the HNB requires termination of additional core network (CN) interfaces in the HNB. This will lead to an undesired increase in complexity of HNB implementation. In addition, such additional terminations of CN interfaces in local IP access devices may harm implementation of local IP mobility in future local area scenarios by necessitating gateway relocation procedures on every inter access device handover in case of terminal movements within a local service area (e.g. office or campus LAN with multiple local area access devices (e.g. (base) stations).
As another issue, HNBs are no high availability nodes and may thus suffer from power failures or broadband access breaks. End users may switch them off anytime for energy saving purposes while they are not at home. This would add complexity to network exception case handling if CN interfaces were terminated in co-located gateways at such HNBs.
An even further issue is that according to the current standard a terminal device shall have only one serving gateway as a mobility anchor to the EPC at a time. In case a real local gateway is provided and controlled via a CN interface, there would be two gateways for each terminal, i.e., one in the EPC as usual and another co-located with the HNB, which is not desirable.
The WO2008/125729A1 discloses a method, radio system, mobile terminal and base station for providing local breakout or local IP access, wherein local access session or service management is performed at EUTRAN (Evolved Universal Terrestrial Radio Access Network) level when the need for core network interfaces to control the local gateway functionality can be eliminated. However, radio resource control (RRC) and non-access stratum (NAS) interfaces still need to be modified accordingly, which might lead to support or compatibility related problems.